A pseudo wire (Pseudo Wires, PW) is a mechanism for carrying a key element of an emulation service from one PE (Provider Edge, provider edge) device to another or multiple other PE devices through a PSN (Packet Switch Network, packet switch network). Through tunnels on the PSN network, such as an IP (Internet Protocol, Internet protocol), an L2TP (Layer 2 Tunneling Protocol, layer 2 tunneling protocol) or an MPLS (Multiprotocol Label Switching, multiprotocol label switching), the PSN may transmit a data payload of multiple types of services by emulating multiple types of services such as an ATM (Asynchronous Transfer Mode, asynchronous transfer mode), TDM (Time Division Multiplexing, time division multiplexing), and Ethernet (Ethernet). FIG. 1 is a schematic diagram of a network reference model of a point-to-point pseudo wire. Two provider edge devices PE1 and PE2 provides customer edge (Customer Edge, CE) devices CE1 and CE2 that are connected to the PE1 and the PE2 with one or multiple PWs, so that corresponding CEs may communicate with each other on the PSN. An internal data service borne by the PW is invisible to a bearer network, that is, for the bearer network, a CE data stream is transparent. A local data unit (such as bit, cell or packet) reaching through an AC (Access Circuit, access circuit) is first encapsulated in a PW protocol data unit (PW-PDU), and then is transmitted in a lower-level bearer network through a PSN tunnel. The PE executes necessary encapsulation and de-encapsulation processes on the PW-PDU, and any other functions (functions such as sorting and timing) required by a PW service.
There are mainly three optional outer-layer tunnel modes for PW encapsulation, which are respectively an IP/UDP (User Datagram Protocol, user datagram protocol) mode, an L2TP mode and an MPLS mode. An access network and a metropolitan area Ethernet are generally layer 2 devices. If it is required to support PWE3 (pseudo wire emulation edge-to-edge, pseudo wire emulation edge-to-edge), not only a control plane of a layer 2 network node needs to be improved to upgrade the control plane to layer 3, but also a data plane of the layer 2 network node needs to be improved to upgrade the data plane to a layer supporting MPLS or IP, which brings high complexity to the access device and the metropolitan area Ethernet, and causes a high cost and poor scalability (Scalability).